This proposal is integral to the overall PPG theme to study fetal and adult adaptations to long-term hypoxia (LTH) at high altitude. Protection is needed against cerebral insults not only in the adult but also in the fetus exposed to systolic hypertension during LTH. Adrenergic neurons, arising from the superior cervical ganglion (SCG), are an important component of the regulation of cerebral blood vessel contractility and blood flow under this stress. Furthermore, these neurons regulate cerebral blood flow under stress conditions such as hypoxemia and hypertension, reducing the risk of stroke, and attenuating severity of pathology following subarachnoid hemmorhage. Our earlier published data show that adrenergic nerve function in middle cerebral arteries (MCA) is facilitated via neuronal nitric oxide synthase (nNOS) containing nerves co-innervating the cerebral vasculature. These data suggest that there is a complex communication pathway between these two nerve types. We now are focusing on the SCG as it is a well established and efficient model for studying the complex processes that control intracellular calcium ([Ca2+]i) in adrenergic nerves and modulation by nNOS nerves. The function of adrenergic nerves depends in part on calcium induced calcium release (CICR) from the smooth endoplasmic reticulum (SER). CICR amplifies increased [Ca2+]i caused by influx through Ca2+ channels and requires that SER be filled by Ca 2+ influx through store operated Ca2+ channels (SOCC) and SER Ca 2+-ATPases (SERCAs). The faciliatory function of nNOS nerves on adrenergic nerves in the SCG may, in part, be due to amplification of the CICR process. We have shown that the function of faciliatory nNOS nerves declines during LTH at high altitude, which is partly related to a decline in nNOS protein levels. These observations may have implications for the distribution of blood flow during LTH acclimatization at high altitude. Studying mechanisms underlying the regulation of adrenergic nerves is vital to human health and development -- from fetus to adult. The project goal is to determine mechanisms underlying the impact of LTH and development on intracellular calcium ([Ca2+]) signaling in adrenergic neurons arising from the SCG and modulation of these processes by nNOS nerves. The governing hypothesis is: positive modulation of adrenergic nerves via nNOS nerves through the CICR process or refilling of SER Ca 2+ stores declines in response to LTH, We will use a range of techniques, instrumental, pharmacological and molecular to probe the mechanisms by which LTH stress may alter the refilling of SER Ca 2+ stores and/or the signaling pathway responsible for modulating CICR in isolated sheep SCG cells. The four groups to be studied are: adult non-pregnant normoxic and high altitude acclimated, and near term fetus, normoxic and high altitude.